We used the detected pulsation modes and adiabatic pulsation models to do seismology of the class of ZZ Ceti stars and measure the H layer mass for 83 stars. We found the surface hydrogen layer to be within the range 10−9.5 ≥ MH/M* ≥ 10−4, with an average of MH/M* = 10−6.3, which is thinner than the predicted value of MH/M* = 10−4, indicating that the stars lose more mass during their evolution than previously expected. These results are preliminary and do not include the possible effects of realistic C/O profiles on the fits.